A conventional buried distribution network of pipes for conducting natural or produced gas from a public utility throughout a city and into homes or buildings for heating purposes includes large diameter gas mains extending beneath and along the city streets, from each of which many smaller diameter gas service lines extend laterally, each for delivering the gas into a house or other building. In low pressure systems for delivering the gas at a pressure of about 6"-water column (0.25 p.s.i.g.) each such service line is usually made of from 11/4"-diameter to 2"-diameter or larger pipe, whereas in higher pressure systems (e.g., 48"-water column, or 2.0 p.s.i.g.) the diameter of the service line may be 1/2", or 3/4", or larger. The service line extends some 25 to 50 feet underground from a tee connection on the top centerline of the gas main to and through the building wall, and into the basement. Ordinarily there is no manhole located at the main tee connection, so that the tee as well as the service time itself is inaccessible without excavation, being buried several feet under the paved street. The steel pipe of which the service line is made passes beneath any sidewalk, lawn, garden and the like, all being ground areas which are not intended to be disturbed. A curb valve, normally of the gate type and accessible by way of a street level valve box, may or may not be located within the service line to shut off gas glow when desired.
When because of breakage or corrosion one or more leaks develop in such a service line, a common repair technique is to install an internal conduit, usually made of metal or plastic tubing, to carry the gas past the leak points. The installation is usually made working mainly from the basement or service end of the line, and extends all the way to the main. Some street excavation has been required to reach the tee connection at the gas main, both to shut off the flow of gas from the main and to open the service line to make the required interior connection between the liner tubing and the service line adjacent to the main, thus to avoid replacement of the service line as would entail digging and trenching along much if not all of its length.
A common technique for connecting a plastic liner tubing at the street end of a conventional steel service line involves removal of a short section of the service line adjacent to the main, and substitution of a prefabricated steel pipe adapter section to which a length of the plastic liner pipe has already been permanently joined, as by a compression coupling formed integrally with the adapter section. In this procedure, after the required street excavation to locate the gas main tee connection, and after the flow of gas from the main has been stopped and the required length of the existing service line has been removed, the plastic liner pipe is fed through the service line from the building basement and its foward end is connected to the adapter section. The latter is then connected to the tee-fitting on the main. Having thus connected the liner conduit at the street end, the service end of the liner pipe is connected to the interior of the service line at the point where it projects into the basement through the building wall, and a variety of service head adapters and techniques are known for doing so without any excavation adjacent to the building. Of course, before installing the liner the interior of the service line must be cleaned of dirt and scale by reaming as necessary, including possible reaming through any curb valve in the line.
In general, such interior by-pass installations requiring excavation at the gas main are known, and are shown for example in U.S. Pat. Nos. 2,268,263 (Newell et al.) and 2,546,348 (Schuman). Similar installations which are intended to be made working solely from the basement or service head end of the service line, thus requiring no street excavation at all, are disclosed for example in U.S. Pat. Nos. 2,731,041 (Mueller et al.); 2,756,779 (Tratzik et al.); and 2,829,675 (Mueller et al.), although in these patents only relatively short lengths of the liner pipe are described as extending only a short distance outwardly from the building wall rather than over the entire distance to the gas main as contemplated by the present invention. All of the foregoing as well as other patents, such as U.S. Pat. Nos. 2,487,939 (Norton); 2,641,491 (Mueller et al.); and 3,244,438, describe a variety of adapters for connecting and hermetically sealing the liner tubing to the service head end of the service line in such internal by-pass systems.
However, known by-pass arrangements which extend all the way from the building to the main are not generally believed to be effectively installed without any steet excavation, and are therefore considered to be very costly in terms of the time, inconvenience and expense involved in such street excavation and in replacing the ground and its cover to its original condition. Regarding known types of interior by-pass installations which do not require street excavation, it is believed that, while they may be effective working with short lengths, they probably cannot be reliably installed where the length of by-pass tubing extends from the building to any location beyond the curb valve, which must be shut or cut off the flow of live gas from the main, because these installations in general are not easily or safely made in a service line in the face of a normal flow of gas, or cannot be tested for leaks.
In known types of interior by-pass installations in which the liner tubing is installed working solely from the basement end of the service line it is especially difficult to secure a fluid-tight seal at the "blind" end of the service line, and to confirm that an effective seal has been made at that end. In fact, in all previous types of installations which extend all the way to the main, an effective technique for leakage testing of the blind end liner seal, working solely from the building basement, has not been developed. Nor has any previous adapter sealing technique permitted effective simultaneous testing of the seals made at both ends of the line, to the end that both can be certified as meeting test standards established for such seals.
In addition, previous interior by-pass liner installations are usually required to be made using considerable care or skill, with attendant high cost due to the prolonged time involved in making and testing the installation. Of course, there is a commensurately long interruption in gas service to the building, resulting in other inconveniences.